At present, the main transformer foundation of 110kV substation mostly adopts cast-in-place concrete foundation, which has many problems, such as many processes, complex construction, long construction period and difficult to guarantee construction quality. In view of the above problems existing in cast-in-place main transformer foundation, and according to the stress condition of 110kV main transformer foundation and the requirements of installation on-site, a new type of assembled orthogonal diagonal grid raft foundation is proposed, which can effectively avoid the above defects of cast-in-place main transformer foundation. Firstly, the finite element analysis method was used to establish a refined model to study the factors affecting the mechanical performance of the connection joints of the fabricated grid raft foundation. Based on the comprehensive comparative analysis, the connection mode and structural measures of the connection joints of the fabricated grid raft foundation were proposed; Secondly, the model was made, and the flexural and shear properties of the connection joints of the fabricated grid raft foundation were studied by using the indoor test method, and the results were compared with the finite element calculation results. The results show that the bearing capacity of the prefabricated grid raft foundation connection mode has a high safety reserve, which verifies the feasibility of the connection mode proposed in this paper and the reliability of the mechanical performance. The research results can not only meet the design requirements of 110kV main transformer for foundation, but also be further applied in other structure foundations.